The LTE-A (Long Term Evolution-Advanced) is a further evolved and enhanced system based on a 3GPP LTE (3rd Generation Partnership Project Long Term Evolution) system. In this system, the downlink radio access technique may be Orthogonal Frequency Division Multiplexing (OFDM) or Orthogonal Frequency Division Multiple Access (OFDMA), and the uplink radio access technique will be Single-Carrier FDMA (SC-FDMA) which is a type of a linearly pre-coded OFDMA.
The uplink system band has a structure where a Physical Uplink Control Channel (PUCCH) is used for transferring uplink control messages where there is no uplink user traffic, and a Physical Uplink Shared Channel (PUSCH) is used for transmission of uplink user traffic. Additional control messages may be transmitted in resources initially allocated to the PUSCH. The PUCCH carries uplink control information, such as ACK/NACK messages, channel quality indicators (CQI), scheduling request indicators (SRI), channel rank indicators, downlink pre-coding information, etc.
The downlink system band has a structure where a Physical Downlink Shared Channel (PDSCH) is the primary data bearing channel which is allocated to users dynamically. The PDSCH carries data in transport blocks (TBs), which correspond to a media access control (MAC). The TBs are passed from the MAC layer to the physical (PHY) layer once per transmission time interval (TTI).